What Saturn does in a chart
Saturn is the part of the chart that answers one question:What do I have to work at over time? It describes structure and commitment — not events, and not outcomes.
What Aries does to it
Aries is a fire sign, so it moves on impulse and enthusiasm. It is also cardinal, which means it starts things. Put those together with Saturn and you get works at aries themes — direct, quick to start, applied specifically to structure and commitment.
Aries is ruled by Mars, so this placement tends to be coloured by drive and desire as well.
The useful version
Placements are not verdicts. This one describes a default setting, not a limit — the things listed above are what you do when you are not thinking about it, which is exactly why noticing them is worth something.